Oatmeal bottle

Tips for formula feeding and adding oatmeal? My son is almost 3 months old and it was recommended by his pediatrician we add oatmeal to his bottle because of his reflux. We tried his first bottle this evening we use Avent bottles. Well we cut a small slit in it and I feel it went WAY too fast because it was a 5 oz bottle and I had to keep removing it from his mouth because he was taking down an ounce at a time within seconds. I just need help on how to get the flow right. He of course spit up afterward so I almost wanna give up on the oatmeal as well but it was just the first bottle. Any advice?

Also, I don’t want any bashing. If you don’t agree with this move on please. Rude comments will be deleted. 🤷🏻‍♀️🤷🏻‍♀️